Rheostat.



Patented Oct, 29, [90L T. S. PERKINS.

R H E 0 S T A T.

(Applicatiun filed Nov. 9, 1900,)

(No Model.)

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' UNITED STATES PATENT OFFICE.

THOMAS S. PERKINS, OF IDLEWOOD, PENNSYLVANIA, ASSIGNOR TO THE WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPO- tATION OF PENNSYLVANIA.

RH EOSTAT.

SEECIFICATION forming part of Letters ;Patent N 0. 685,485, dated October 29, 1901.

Application filed November 9,1900. Serial No. 35,994. (No model.)

To all whom it may concern Be it known that I, THOMAS S. PERKINS, a citizen of the United States, residing at Idlewood, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Rheostats, of which the following is a specification.

Myinvention relates to apparatus employed in connection with the operation of electrical machinery for varying the currents supplied thereto, and has for its object to provide a rheostatelement or resistance-box of simple and inexpensive construction and one that shall be efficient and durable in use.

In the operation of electrical motors, particularly those employed for driving railwayvehicles, the large and frequent variations in speed ordinarily involves the employment of a considerable amount of ohmic resistance, which is cut in and out in accordance with the exigencies of the service. In order that the amount of resistance may be varied over a considerable range, several independent elements are usually employed, these elements being usually of the same construction and capacity and being severally cut in and out of circuit by means of a controlling-switch.

My present invention comprises a rheostat element for use in the manner above indicated and is illustrated in the accompanyingdrawings, in which Figure 1 is a side elevation of the invention. Fig. 2 is a plan view of the device shown in Fig. 1; and Fig. 3 is aview, partially in end elevation and partially in section, of said device.

The details of construction as illustrated are as follows: The frame 1 is of skeleton construction in order to fully expose the supported parts, so as to facilitate dissipation of heat, and may be conveniently made of castiron. The subelements of each resistanceboX or rheostat elements are in the form of grids 2 of zigzag formation, so as to provide a maximum length of conducting-path for a minimum amount of space occupied, and these grids will generally be formed of castiron in order to keep the cost of material and the expense of manufacture as low as possible, though any other metal or alloy having a suitable resistance and temperature coeflicient may be employed. It is well known that cast-iron is a good resistance material; but difficulty has heretofore been experienced in its use as a resistance medium by reason of the impracticability of forming castings of very small cross-section, as well as the difli-.

culty in so supporting the grids as to avoid distortion and breakage, particularly where the rheostat is subjected to jolting, as is the case when mounted upon a railway-vehicle. In order to employ grids the bars of which are of as small cross-section as it is possible to make an iron casting, I provide the top and bottom of the grid with supporting and strengthening bars 3 of non-conducting and heat-resisting material. I fasten the ends of these bars 3 securely to the extremities of the end bars or limbs of the grid by means of screws. The extremities of the intermediate bars or limbs of the grid are severally provided with projections 2, that fit into corresponding holes or sockets 3 in the supporting and strengthening bars 3. By this means the limbs are held in proper relation and at the same time free expansion is permitted without subjecting the parts to strains. I have found compressed asbestos to be a desirable material for the bars 3, but do not limit myself to the employment of this specific material. In order to rigidly support the grids, I form each of them with a relatively heavy bar 4 at each end and enlarge this bar for some distance at each side of its middle point, as indicated at 5. In recesses 6 in the frame 1 I mount slabs 7, of slate or other suitable non'conducting and heat-resisting material,to which the portions 5 of the grids are bolted.

As shown in the drawings, the grids are connected in series by means of inverted-U- shaped strips or bands 8 of good conducting material, which fit over the slabs 7 and have their inner arms interposed between the faces of the parts 5 and the slabs and their outer arms connected in pairs by means of plates 9 of good conducting material, which alternate in position from side to side of the frame. It will be readily understood without further illustration that a multiple or a multiple-series connection of the grids may be effected by employing plates 9 of greater length and so locating them as to span the proper number of grids to secure the desired circuit relations. The bolts 10, which support the grids, pass through the plates 9 and strips 8, as shown. The terminal connections to the grids may be made by means of any suitable binding devices, those here shown being blocks 11, fastened to the end strips 8 and slab 7 by screws and having holes or sockets 12 for. the conductors and bindingscrews 13 for fastening the ends of the conductors firmly in position in the sockets. While the terminal blocks are shown as attached to the end strips 8 at one side of the frame, it is obvious that they may be at tached to any other two strips and at either the same side or at opposite sides of the frame, according to theamount. of resistance desired and other conditions of use.

It will be seen from the illustration and foregoing description that the grids 2 are independently and firmlysupported in position and are so provided with insulating and protecting devices that there is no danger of destruction or injury either by breakage of the parts or by the establishmentofshort circuits.

Variations in the details of construction may obviously be made without departing from my invention, and I therefore desire it to be understood that the invention is not limited except as specified in the claims.

I claim as my invention 1. A resistance-box comprising a frame and a plurality of electrical resistance-grids mounted therein and severally provided at the respective ends of the grid-bars with supporting and strengthening bars of non-corn ducting material.

2. A rheostat element comprising a frame and a plurality of electrically-com]ected grids mounted therein and severally provided at the respective ends of the grid-bars with strengthening-bars of non-conducting material.

8. A rheost-at element comprising a frame having plates or slabs of non-conducting material at its sides and a plurality of electrically-connected resistance-grids fastened to said slabs or plates and provided at the respective ends of the grid-bars with strengthening-bars of non-conducting material.

4. A grid or rheostat element of zigzag formation and provided at tlte ends of its bars rial at the ends of their bars.

7. A rheostat element comprising a frame, a plurality of resistance-grids of zigzag formation mounted therein and severally provided with projections at the extremities of their bars or limbs and non-conducting bars rigidly fastened at their ends to the extremities of the end bars or limbs of the grids and having holes to receive the projections on the intermediate bars or limbs.

8. A resistance-grid of zigzag formation having projections at the extremities of its limbs or turns, except those at its ends, and bars of non-conducting material fastened to the extremities of the end limbs and having holes in which the intermediate projections fit.

9. A rheostat element comprising a skeleton frame having non-conducting slabs, a plurality of resistance-grids having strengthening-bars, conducting-strips, means for fastening said strips and the grids together and to the slabs, conducting-plates for connecting the outer ends of the strips in accordance with the circuits desired and detachable terminal blocks fastened to two of the conducting-strips.

10. A rheostat element comprising a frame, a plurality of resistance-grids of zigzag formation arranged side by side in said frame, removable conducting strips and plates for connecting said grids in circuit with each other, detachable terminal blocks for conmeeting the grids to an external circuit and strengthening-bars in engagement with the extremities of the grid bars or limbs.

In testimony whereof I have hereunto subscribed my name this 5th day of November, 1900.

THOMAS S. PERKINS.

Witnesses:

WESLEY G. CARR, BIRNEY HINEs. 

